Enhanced spontaneous calcium efflux and decrease of calcium-dependent calcium release from the isolated perfused heart of spontaneously hypertensive rats


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Abstract

Objective:The aim of this study was to clarify the further details of calcium handling in hypertension.Design:By preserving the physiological environment of cell membrane, whole hearts were used for comparison of calcium flux between spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats.Methods:Hearts from SHR and WKY rats were perfused with Krebs–Henseleit solution under constant flow and the effluent collected.Results:After labelling of the heart with 45Ca2+ (100µmol/l), 45Ca2+ binding was found to be saturated, and washing with calcium-free perfusion solution showed two exponential curves for calcium dissociation, indicating a fast (α-) and slow (β-) phase. The half-lives of the β-phase for both 4- and 8-week-old SHR were significantly shorter than those for age-matched WKY. Also in this phase, infusion of non-radioactive Ca2+ caused a transient dose-dependent release of 45Ca2 +. A significant reduction in the amount of 45Ca2+ release induced by 2mmol/l Ca2+ was observed in both 4- and 8-week-old SHR compared with age-matched WKY rats. Infusion of lanthanum, caffeine, ionomycin (calcium ionophore) and treatment of the hearts with ethyleneglycol-bis-(β-aminoethylether)-N,N,N,',N'-tetraacetic acid did not alter 45Ca2+ release by non-radioactive Ca2+. From these observations, 45Ca2+ is presumably released from the intracellular calcium pool, and not from extracellular binding sites or sarcoplasmic reticulum.Conclusions:These findings suggest that an abnormal calcium-handling defect (enhanced calcium efflux and reduction of membrane-bound Ca2+) exists under physiological conditions before and after the onset of hypertension, and that this may be a primary characteristic of SHR.

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